1. Field of the Invention
The invention relates generally to the field of medical equipment, and more particularly relates to a self-destructing syringe system that incorporates safety improvements into hypodermic syringes that are used, for example, to administer injections or take blood samples. These improvements are designed to provide a single integrated safety syringe system which prevents the reuse of the syringe and at the same time protects medical personnel administering medications through the needle (or sampling bodily fluids using the syringe) from inadvertent contamination as a result of a "needle stick".
2. Description of the Related Art
There is presently and has for some time been a need to have low cost commercially available safety syringes which are disposable and cannot be reused. This is particularly true because a large number of injections of medicinal or other substances need to be carried out by patients themselves, that is to say, without the assistance of medical practitioners, under conditions which do not permit an effective sterilization of the syringe before it is used. Even where medical practitioners are available to administer injections, disposable, self-destructing devices are desirable to prevent the reuse of syringes by, for example, individuals addicted to drugs who might utilize such devices discarded as medical waste.
While single use disposable devices are well known which do protect patients from the danger of infectious diseases, such as AIDS and certain hepatitis viruses, they are not known to be included in combination with, nor are they part of, a single integrated low cost safety syringe system which includes (1) efficient means for allowing fluids to be mixed in the syringe prior to the delivery of an injection; along with (2) effective means for protecting medical and hospital personnel from infection due to accidental contact with a contaminated needle or other portion of the disposable apparatus.
For example, hypodermic needles are usually equipped with a removable cap that protects and helps keep the needle sterile. The cap is usually replaceable to cover the used, contaminated needle and prevent accidental needle sticks. However, accidental needle sticks during recapping have long been a problem. Because of tension, time pressure, or fatigue, needle sticks during recapping occur with alarming frequency despite frequent warnings to be careful, and they account for the majority of accidental needle sticks.
Eliminating recapping will not solve the problem because the uncapped needle is so dangerous. Indeed, a large number of accidental needle sticks are caused by uncapped needles found in beds, on floors, or in garbage cans. Even where there is a no recapping policy, the needles are often recapped because of these dangers.
Accidental needle sticks are serious because they can spread disease, including hepatitis, venereal diseases, and of most recent concern: AIDS. A needle stick causes fear and anxiety in the victim. Both the victim and the patient may be subjected to a battery of expensive, time consuming tests. Accidental needle sticks during recapping can cost even a relatively small health care institution thousands of dollars annually. Even worse than the economic cost, however, is the transmission of disease.
For example, the victim of a needle stick from a needle contaminated by an AIDS patient must be repetitively tested for several months after the accident. It is documented that after such a needle stick, the victim may test positive for exposure to the AIDS virus, even if the disease is not contracted. A positive test would cause great fear and anxiety in the victim, would seriously disrupt the victim's personal life, and might even end a victim's ability to work in health care.
Despite the very serious nature of the problem, and the severity of the consequences, the problem has persisted for many years without any satisfactory solution.
Various sheaths that can be slid down over the needle after use have been patented, for example those disclosed in U.S. Pat. No. 4,425,120, U.S. Pat. No. 3,780,734 and U.S. Pat. No. 2,571,654. However, these devices are to complicated, and to difficult and expensive to manufacture, and have never been widely available.
Masters et al, in U.S. Pat. Number 4,654,034, issued Mar. 31, 1987, proposed a safety needle cap comprising a generally cylindrical, hollow tubular body section having a closed first end and an open second end for receiving the needle, and a funnel-shaped lip surrounding the open end and projecting radially and axially outwardly to channel needles into the open end and protect fingers gripping the cap. The cap taught by Masters et al also includes a guard to space fingers away from the open end. The flared ends of the cap and the guard are designed to protect against needle sticks.
In addition to Masters et al, Jennings, Jr. et al, in U.S. Pat. No. 4,643,199; Burke in U.S. Pat. No. 3,333,682; and Ikeda, in U.S. Pat. No. 4,428,246, all disclose needle covers having flared open ends to help protect against needle sticks. However, none of the improvements taught by the aforementioned patents are taught in combination with or as part of an integrated self destructing safety syringe system which simultaneously protects the syringe user from accidental needle sticks, allows for fluids to be mixed in the syringe system prior to delivery, etc.
Knight, in U.S. Pat. No. 3,245,567, is representative of prior art which teaches the use of thumb grips on a sterilized needle storage container using a flared needle cover to give additional protection against accidental needle sticks when sealing the container. However, Knight does not teach the use of a flared needle cap with thumb grips as part of a safety syringe system, nor does Knight address the other desirable aspects of an integrated safety system as mentioned hereinabove, namely the ability to perform fluid mixtures within utilizing the syringe system, self-destruction of the syringe after use, etc.
Syringes intended for being used only for a single injection are also known. For example, French patent application no. 76 12 199 describes a combined ampoule and syringe, in which a piston carries, at its end placed inside the cylinder of the syringe, a joint which is separable from the piston, which is designed to remain in its final position at the bottom of the cylinder when the injection has been carried out. A retraction of the rod causes a separation between the rod and the joint of the piston.
The syringe described in the aforementioned French Patent Application does not, however, permit a liquid to be drawn in from an ampoule. On the other hand, in the construction as proposed by the French Patent Application, it would be an easy matter to remove the joint or packing of the cylinder from the syringe by other means and to use the syringe again after having refilled it.
German patent application no. 17 66 748 proposes a syringe in which the rod is provided with a locking device for preventing the return of the piston from a position of maximum insertion. Nevertheless, this arrangement, situated outside the cylinder, can be easily detached or made inoperative, so that this syringe does not give any guarantee for it not to be used again.
An effectively disposable syringe is described in French patent application no. 75 15 412. It comprises means associated with that part of the piston which is disposed inside the cylinder; but permitting only a single intake and ejection movement of the piston.
As indicated hereinabove, it is frequently necessary to effect the injection of a mixture of several different liquid substances, which mixture cannot be prepared in advance, but only at the moment of injection. This involves the necessity of having available a syringe which is capable of being filled in several steps, that is to say, a syringe of which the piston can carry out an indefinite number of reciprocating movements during the filling of the cylinder before the operation of injection.
Staempfli in U.S. Pat. No. 4,391,272, issued Jul. 5, 1983, addresses the problem of mixing liquids in a disposable syringe prior to injection by proposing a syringe comprising a cylinder of which one end is provided with a nozzle permitting the fixation of a needle, an intake and delivery piston comprising a body arranged so as to form a tight movable partition capable of sliding inside the cylinder, a rod fast with the body of the piston and permitting the latter to be displaced with a sliding movement in the cylinder, and means, cooperating with a groove that is cut or otherwise formed in the body of the cylinder, for preventing the rearward return of at least a part of the body of the piston when the said body occupies a position close to its position of maximum insertion into the cylinder.
In particular, Staempfli proposes several alternate embodiments of a syringe system which is disposable and addresses the problem of mixing liquids within the system; however, all of the embodiments taught by Staempfli require the cylindrical body portion of the system to have a groove formed therein for either (1) engaging the rim of the piston to prevent withdrawal of the piston and reuse of the syringe; (2) retaining a detachable 0-ring sealing joint fitted onto the piston body during the manufacturing process; or (3) receiving a disengagable packing or sealing joint fitted onto the piston body during the manufacturing process.
It would be desirable to have a safety system that includes the benefits of the system described by Staempfli, i.e., one that is disposable and which allows for the mixing of fluids within the system. However, it would also be desirable if such a system did not have to rely upon costly and tolerance sensitive manufacturing processes associated with forming Staemplfi's grooves within the syringe cylinder bodies. For example, the reuse prevention mechanism taught by Staempfli, namely the grooves into which the various deformable members must fit and be retained, can be easily defeated if not manufactured to precise specifications which allow the deformable members to be accepted and held therein.
Finally, Butterfield in U.S. Pat. No. 4,493,703, issued Jan. 15, 1985, teaches a hypodermic cartridge with a drive piston rendered non-retractable by including on it a resilient disc-like element, having a diameter slightly larger than the glass tubular body of the syringe, which acts as a continuous pawl. Any attempt to retract the drive piston jams the edge of the resilient element against the inside wall of the tubular body.
Although providing means for preventing retraction of a piston within a syringe, Butterfield is expressly directed to syringe systems which are not capable of solving the aforementioned fluid mixing problem. It is in this context that the Butterfield invention is described and in fact Butterfield's preferred syringe cartridge (which does not permit fluid mixing) utilizes a detachable actuator rod/piston assembly to assure piston non-retractability.
Moreover, all the preferred embodiments of the invention illustrated in the Butterfield patent teach a threaded actuator rod simply fitted over an unthreaded shank portion of the piston to assure detachment of the actuator rod if an attempt is made to retract the piston at any time. Such an arrangement is incompatible with syringe systems that provide for the desirable capability of mixing of fluids, as, for example, the system taught by Staempfli.
It should be noted that a "less preferred" embodiment of the Butterfield invention disclosed in U.S. Pat. No. 4,493,703, as an aid against piston retractability when the actuator rod and the piston are actually attached to one another, relies on the inside surface of the tubular member portion of the syringe including a number of longitudinally spaced ratchet teeth to engage the resilient disc. This arrangement, although designed to prevent retraction of the piston, is characterized by Butterfield as (1) being difficult to manufacture and (2) less preferred then embodiments that have the actuator rod sitting on the unthreaded shank, since the disc like elements contemplated by Butterfield, in Butterfield's words, "could probably be overpowered by the application of brute force on a fixedly attached piston".
Accordingly, since the Butterfield syringe is not compatible with devices that are used to mix fluids; does not teach the aforementioned desirable needle stick prevention safety features; does not teach these features in combination with a syringe that has an inherent self destruct capability to prevent reuse (for example, Butterfield's detachable actuator rod can be reseated on the piston assembly effectively reconnecting it thereto when an unthreaded shank is used on the piston); and is admittedly difficult to manufacture, it would be desirable to provide a self destructing safety syringe system that solves all of the aforementioned problems inherent in not only Butterfield, but in all of the known prior art syringe systems, whether taken individually or combined.